我们都曾在当时看似做出了明智的选择，事后却演变成了棘手的难题。瑞典在20世纪60年代就做过类似的事。当时引进了信号螯虾，旨在促进渔业发展。据瑞典农业科学大学（SLU）称，这一举措对本土的贵族螯虾造成了灾难性后果。自外来物种到来以来，本土种群数量已下降了四分之三，且外来物种携带一种对贵族螯虾致命的疾病。
We all have made a seemingly smart choice at the time that later turned into a headache. Sweden did something like that in the 1960s. It brought in the signal crayfish, a species introduced to support fishing. According to the Swedish University of Agricultural Sciences (SLU), the move proved catastrophic for the native noble crayfish. Native populations have dropped by a factor of four since the newcomer arrived, and the newcomer carries a disease that is deadly to them.A fishing boost that came with a catchThe signal crayfish did deliver on fishing.
渔业增产伴随隐患信号螯虾确实兑现了渔业增产的承诺。它在瑞典南部提供了良好的捕捞机会，并在耶尔马伦湖和韦特恩湖建立了可捕捞的种群。那里的商业捕捞量大幅增加，主要是因为捕捞活动增多。但信号螯虾是螯虾瘟疫的慢性携带者。这意味着它携带病菌且往往能存活下来，这与贵族螯虾截然不同。
It has provided good fishing opportunities in southern Sweden, and built fishable populations in lakes Hjälmaren and Vättern. Commercial catches there have increased sharply, mostly because there is more fishing. But the signal crayfish is a chronic carrier of the crayfish plague. That means it carries the disease and often survives it, not like the noble crayfish.
瘟疫如何在湖泊中传播螯虾瘟疫是一种仅影响淡水螯虾的真菌性疾病。它通过孢子在动物间传播。贵族螯虾感染后会迅速死亡；信号螯虾往往能存活并传播病菌。这就好比有人带着感冒病毒却不发病，周围的人却纷纷染病。如果受到污染、食物短缺、过度拥挤或不利水温等压力因素影响，信号螯虾也会发病。潮湿的捕鱼装备、其他器具、饵料鱼以及水中的孢子也能传播瘟疫。
How the plague travels through a lakeCrayfish plague is a fungal disease that affects only freshwater crayfish. It spreads through spores between animals. The noble crayfish dies quickly when infected; the signal crayfish often survives it and transmits it. Think of someone who carries a cold without getting sick, while everyone around them does. Signal crayfish can still get sick if stressed by pollution, poor food supply, crowding, or unfavorable water temperatures. Wet fishing gear, other equipment, bait fish, and spores in the water can also carry the plague.
濒临灭绝的本土物种贵族螯虾的衰退始于20世纪初，主要归因于瘟疫。瑞典农业科学大学估计，过去一个世纪里，其种群数量多达97%已被消灭。它在瑞典濒危物种红色名录中被评估为极危物种。酸化、污染和水位调节都导致了种群下降，但信号螯虾加速了这一进程。
A native species on the edgeThe decline of the noble crayfish started in the early 20th century, mainly due to the plague. SLU estimates up to 97 percent of its population has been wiped out in the past century. It is assessed as critically endangered on the Swedish Red List of Threatened Species. Acidification, pollution, and water regulation all contributed to the decline, but the signal crayfish accelerated it.
1994年至2007年间，近千个湖泊、河流和水道受到瘟疫侵袭，仅诺尔博滕省完全幸免。损失也波及钱包。市场上贵族龙虾的价值是信号龙虾的两倍多。
Between 1994 and 2007, almost a thousand lakes, rivers and watercourses were affected by the plague, and only Norrbotten County has been completely free. The loss also hits the wallets. The noble crayfish is worth over twice as much as the signal crayfish on the market.A problem bigger than SwedenSweden is not unique.
并非瑞典独有的问题瑞典并非孤例。大卫·霍尔迪希及其同事在2009年发表于《水生生态系统知识与管理》的一篇综述中发现，欧洲的非本地物种数量现已超过本地物种两倍。栖息地丧失、水质恶化、过度捕捞和气候变化也是威胁，但最重要的威胁是非本地龙虾和龙虾瘟疫。水族贸易是新物种进入的另一途径。一些国家正在建立安全的“方舟”栖息地以保护本地龙虾。
In a review published in Knowledge and Management of Aquatic Ecosystems in 2009, David Holdich and colleagues found that non-native species now outnumber native species in Europe by two to one. Habitat loss, poor water quality, overfishing and climate change are also threats, but the most important are non-native crayfish and the crayfish plague. The aquarium trade is another route for new species. Some countries are setting up safe ‘ark’ sites to protect native crayfish.
瑞典和垂钓者能做什么？瑞典已收紧对龙虾引入的限制。瑞典农业大学表示，尽管早在1994年就禁止引入，但非法放流现象依然存在。信号龙虾于2016年被列为入侵物种，现在养殖该物种或将其引入新水域均属违法。垂钓者也能帮忙。瑞典农业大学建议，在转移水域前彻底晾干船只、捕虾笼、靴子和其他装备，仅使用来自垂钓水域的饵料鱼，或将其冷冻一天。这个故事展示了移动一个物种如何最终改变整个生态系统。
What can Sweden and anglers do? Sweden has tightened restrictions on crayfish introductions. SLU says illegal releases have persisted even though introductions were prohibited as early as 1994. The signal crayfish was designated an invasive species in 2016, and it is now illegal to farm the species or introduce it to new waters. Anglers can help too. SLU recommends completely drying boats, traps, boots, and other gear before moving between bodies of water, and only using bait fish from the water you are fishing in, or freezing it for one day. This story shows how moving one species can end up changing a whole ecosystem.